This invention is in the field of integrated circuits. Embodiments of this invention are directed to controlling power supply voltages applied to static random-access memory (SRAM) in such integrated circuits.
Portable computing devices have become very popular in the marketplace in recent years, especially with the widespread deployment of wireless communications. For example, those cellular telephone handsets known as “smartphones” are essentially handheld computers that are capable of Internet browsing, email communications, digital audio and video downloading and playback, creation and editing of office documents, personal schedule and contact management, digital photography, and other functions, in addition to serving as a cellular telephone handset. Many of these smartphones are capable of carrying out data communications over the cellular network (e.g., using “3G” service) and in some cases also over conventional wireless network facilities and protocol (IEEE 802.11x). Both in these smartphones as well as in less capable handsets, a substantial amount of digital data processing is therefore carried out. As such, the electronic circuitry used in these devices often resembles a computer architecture, with a central processing unit, program memory and data memory stored in memory resources of the read-only memory (ROM) and random-access memory (RAM) types, cache memory, peripherals, co-processors, and the like, all of which communicate with one another over one or more system buses.
Power consumption is a critical factor in the design and functionality of these portable devices. Typically, power consumption of the electronic circuitry is reflected in the battery life of these devices, which of course is the time that the system can be operated from full charge until recharging of the battery is required. Battery life is an important factor in the marketplace acceptance of portable devices. In addition, the market also favors those devices offering the most functionality in the smallest physical form factor. However, thermal effects of power consumption constrain the extent to which these handheld systems can be miniaturized. For these and other reasons, it is desirable to minimize power consumption in these high-performance, high-capability, portable computing systems.
Memory resources in large-scale integrated circuits consume a substantial portion of the overall device power, largely because of the number of memory cells (i.e., transistors) involved in writing, reading, and maintaining data and program instructions for the data processing logic and digital signal processor functions. In addition, the substantial internal reactive load of relatively long and numerous row and column conductors in the memory arrays causes significant power dissipation during switching operations.
As known in the art, particularly in modern portable devices such as cellular telephone handsets and smartphones, random-access memory is often realized in the form of static RAM (SRAM). SRAM resources do not require periodic refreshing of the stored data state (as does dynamic RAM), and as such are especially attractive for realization of “embedded” RAM in the same integrated circuit as the programmable logic functions. More specifically, so-called “systems on a chip” that are commonly used to realize much, if not all, of the data and signal processing functionality of modern portable computing devices in a single integrated circuit, typically use SRAM to realize program memory, data memory, and cache memory.